1. The Field of the Invention
The invention is in the field of exercise machines, particularly those intended for home use.
2. The Prior Art
The use of exercise machines has proliferated in the last decade or so. In general there are two main classifications of such machines--those primarily intended for use in a commercial sports center and those primarily intended for use in the home. Those intended primarily for use in a sports center are quite complex, are structurally heavy and bulky, are usually attached to the floor or the wall, and oftentimes have a complicated arrangement of levers, pulleys, weights, etc. Normally they may also be adjustable for different users having different physical strengths. Those intended primarily for the home are simpler, lighter, much less expensive but still adjustable to some degree.
One such exercise machine comprises flexible elastic shock cords, usually two, which are stretched by a force exerted by the user. As a cord is stretched more and more, the force required to stretch it increases more and more. One end of the shock cord is attached to a fixed structure and the other end attached to a booster bar adapted to be moved by the user's arms or legs as the cord is stretched by the user. As a natural consequence of the size of the user the stretched length of the shock cord will be substantially constant for a given user but will be different for a different user. Also as a natural consequence of the physical characteristics of shock cords the force-length curve is an inverse exponential when the force is displayed as the abscissa. Thus the maximum force required for a given user to stretch his arms or his legs to their fullest extent depends on the characteristics of the shock cord and also on the ratio of the stretched length to the unstretched length of the shock cords. Since a different user having a different physical size or strength will require a different ratio of stretched length to unstretched length it becomes necessary to provide some means for shortening or lengthening the unstretched length. This is normally effected by means of clamps; however the clamps oftentimes damage the shock cord and thus make the shock cord essentially unusable after a given number of adjustments. It would be desirable to have an arrangement whereby the unstretched length of the shock cord could be adjusted by the user without the use of clamps or tools.